Tobacco is grown as a row crop with row widths and within-row plant spacings of about 1.07-1.22 m and 0.38-0.56 m, respectively. Most tobacco types are decapitated (topped) when the plants are in the early stages of floral development to increase yield and improve the quality of the cured leaf. Physiologically, decapitation of a dicotyledonous plant, such as tobacco, releases apical dominance, and growth of axillary buds (suckers) is dramatically increased. To obtain the increase in yield and quality desired from topping, the growth of the suckers must be controlled. In the early culture of tobacco, suckers were removed manually. Currently, in most cases, suckers are controlled with chemicals, most commonly fatty alcohols, dinitroanilines, and maleic hydrazide. A common protocol for flue-cured tobacco in the U.S. is to use fatty alcohols at topping, followed by a second application three to five days later, and then followed one week later by a tank mix of a dinitroaniline and maleic hydrazide. The fatty alcohols and the dinitroaniline materials must contact the sucker to effect control, while maleic hydrazide, which acts systemically, must be absorbed through the leaf tissue.
The method of application and the equipment used to control suckers varies with growers, from hand-held equipment to multi-row, over-the-top sprayers. The latter features a 56-cm long boom with a solid cone nozzle in the middle and nozzles at each end angled downward at 45 degrees toward the center of each row. Spraying is continuous as the sprayer moves along the row, the nozzles positioned about 25-cm above the topped tobacco, applying suckercide (chemical agent that suppresses sucker growth) solution (approximately 30 ml/plant).
Others have improved the efficacy of fatty alcohols by using guides to center each plant in the spray pattern, thereby directing more of the spray (chemical) down the stalk. It has been shown that 3 ml of fatty alcohol solution placed in each of the upper three leaf axils of a tobacco plant resulted in a high degree of control. Furthermore, missing any of the three upper axils greatly diminished sucker control down the stalk. In the U.S., this procedure would amount to a 70% reduction of chemical used per application when compared to an over-the-top application.
Based on this information, applicants designed and constructed an apparatus and method that would apply the sucker control chemical directly over the center (i.e., stalk) of the tobacco plant immediately after topping of the plant by the apparatus. The advantages are to: (1) decrease the volume of sucker control chemical used; (2) reduce production costs associated with topping and sucker control; and (3) reduce release of agrichemicals into the environment.